Re-entrant radial choke for cavity resonator with displacing mechanism

ABSTRACT

A re-entrant radial choke used as a variable compressed noncontacting microwave short for terminating the cavity of a cylindrical resonator. The reflecting short comprises a choke assembly of a plunger and a radial plate. The plunger is in the form of a hollow cylinder having an open and a closed end with the open end facing into the cavity. The radial plate is secured to the closed end to form a radial transmission line terminated in a short. Accordingly, the reflecting short is made up of a face of the plunger and a circular short between the plunger open end and the cavity wall.

United States Patent Slevin et a].

[ RE-ENTRANT RADIAL CHOKE FOR CAVITY RESONATOR WITH DISPLACING MECHANISM Inventors: Robert F. Slevin, Rumson; E. Raye Aikins, Point Pleasant, both of NJ.

Harvard Industries, Inc., Farmingdale, NJ. by said Aikins Filed: Nov. 13, .1972

Appl. No.: 305,704

[73] Assignee:

References Cited UNITED STATES PATENTS 6/1956 Hilliard et a]. 333/83 R 4/1954 Collard 333/98 R 3/1955 Ginzton et al, 333/83 R [451 Apr. 23, 1974 Primary Examiner-Archie R. Borchelt Assistant Examiner-Wm. H. Punter Attorney, Agent, or Firm-Maleson, Kimmelman and Ratner [5 7] ABSTRACT A re-entrant radial choke used as a variable compressed noncontacting microwave short for terminating the cavity of a cylindrical resonator. The reflecting short comprises a choke assembly of a plunger and a radial plate. The plunger is in the form of a hollow cylinder having an open and a closed end with the open end facing-into the cavity. The radial plate is secured to the closed end to form a radial transmission line terminated in a short. Accordingly, the reflecting short is made up of a face of the plunger and a circular short between the plunger open end and the cavity wall.

15. Claims, 6 Drawing Figures r I I l \l' l\ F //a v-fi-w/n//// //T l I l /44- /4 I PATENTED APR 2 3 I974 SHEET 3 [IF 3 RE-ENTRANT RADIAL CHOKE FOR CAVITY RESONATOR WITH DISPLACING MECHANISM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention-relates to the field of art of microwave frequency cylindrical resonators.

2. Prior Art It is well known that at microwave frequencies circuit components become so small that they are physically impractical to use. Accordingly, at these frequencies, cavity resonators have been used extensively since they are physically large in size and have a high value of efficiency. Each cavity resonator has a unique value of resonant frequency for each mode of resonance. For a given mode and given cavity shape, the resonant fre quency depends only upon the size of the cavity.

The cavity may be in the form of a cylinder and in an application the cylindrical resonator operates with a signal applied to the wall thereof. If the cylindrical height is at one-half the wavelength of the applied frequency then that frequency is passed. However, if the height is not at one-half the wavelength, then the applied frequency is reflected back or rejected. In order to vary the wavelength of the cylindrical resonator, it has been known to provide as a reflecting short, a moveable plunger which is shorted to the cylindrical inner wall of the resonator. In some of these devices, the plunger directly contacts the inner cylindrical wall by metal fingers thereby providing a metal to metal contact. However, problems have developed since dirt would accumulate between the fingers and the wall thereby decreasing the conductance. Further, the fingers would objectionably scrape the inner wall. Noncontacting plungers have been developed such as radial chokes which provide noncontacting microwave shorts. However, these devices have left much to be desired by the complexity in which they achieve a zero impedance between plunger and inner wall.

,For example, in one device, it has been necessary to use a double bucket type of choke in order to achieve a satisfactory short. Each bucket section is in the form of an open cylinder with the open end of each cylinder facing away from the cavity. A short is produced at the center of each bucket. The circular short travels radially until it reaches the cavity inner wall where itthen travels down the periphery of the choke for a total of a half wavelength. In this manner, there is produced another short at the face of the plunger. However, these prior resonators have left much to bev desired in the large amount of unused room required to accomodate the double structure.

SUMMARY or THE INVENTION A re-entrant radial choke which forms a variable noncontacting reflecting short for terminating the cavity of a cylindrical resonator. The radial choke comprises a plunger and a radial plate. The plunger is formed of a hollow cylinder having an open and a closed end with the open end facing into the cavity of the resonator. The radial plate is secured to the closed end to form therebetween a radial transmission line which is terminated in a short. The short is reflected through the radial transmission lineand the outer periphery of the plunger as a short between said plunger open end and the cavity wall.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified sectional view of a cylindrical resonator embodying the invention showing the basic structure of a choke assembly within a cavity;

FIG. 2 is an enlarged perspective view of the choke assembly of FIG. 1 shown in more detail;

FIG. 3' is an elevational view of the cylindrical resonator of FIG. 1 showing more detail;

FIG. 4 is a plan view of the cylindrical resonator of FIG. 3 with sections cut away;

FIG. 5 is a side sectional view of FIG. 3 taken along lines 55 of FIG. 4; and

FIG. 6 is an enlarged detailed view of portions of the elevational mechanism of FIG. 3 taken along line 6 of FIG. 4.

EMBODIMENTS Referring now to FIG. I there is shown a simplified drawing of a cylindrical resonator 10 having a reentrant radial choke forming a variable reflecting short. The choke assembly comprises plunger 14 and plate '12. The resonant length d of cavity 10a of-resonator 10 is the distance between a face 17 of plunger 14 and a closed bottom 18 of the cavity.

Transmission line 25 applies a microwave frequency signal through a coupling 25a (FIG. '5) which extends into the inner cylindrical wall 11 of iresonator'lO. Output transmission line 26 is coupled (coupling 26a) through wall 11 on a side opposing line 25. If distance d is at one-half the wavelength of the applied signal, then the applied signal is passed or propagated through cavity 10a and transmission line 26. However, if 'distance d is not at one-half wavelength of the applied signal, then that applied signal is reflected back or rejected. By moving plunger 14 up or down within cavity 10a, distance d is varied thereby varying the wavelength of resonator 10. The mechanism for moving'the choke assembly comprising plunger 14. and plate 12 will later be described in detail.

The diameter of inner wall 11 is selected in accordance with a desired mode. For example, a TE mode may be chosen and only applied signals in this mode are propagated through resonator l0. Differeing modes used in cylindrical resonators and cylindrical resonators themselves are described in detail at page 2l9 et seq., Theodore. Moreno, Microwave Transmission Deign Data, Dover Publications, Inc., 1948.

Plunger 14 comprises an open hollow cylindrical choke having a cylindrical wall 19, an open end 19a and a closed end 20. Open end 19a which is the bottom edge of wall 19 faces in a direction into cavity 10a toward cavity-bottom 18, wall 19 is a part of the resonant cavity length. With the open end of the cylinder facing into cavity 10a, plunger 14 is called a reentrant choke.

On the upper face or side 17a of plunger closed end 20 (remote fromopen end 19a) there is formed a solid boss 15. A solid flat cylindrical or radial plate 12 is secured to boss 15 coaxial with plunger 14 with the radius of plate 12 being substantially the same as the radius of plunger 14. Instead of boss 15, other types of separaters may be used such as a radial spacer. Accordingly, a radial transmission line 21 is formed between plate 12 and face 17a having a zero impedance termination formed by outer circular edge 16 of boss 15. Line 21 as well as a line 22 (formed between wall 19 and wall 11) may each be selected to be approximately onequarter wavelength.

Upon application of a signal at line 25 a circular short is produced at 16. This short is reflected out radially until it reaches inner wall 11 then travelsdown the outer periphery of plunger 14 through line 22 until it reaches open end 19a. Since the total distance from circular short 16 to open end 19a is one-half wavelength a reflected circular short is also produced at open end 19a with respect to inner wall 11 of the cylindrical resonator.

It will be understood that a substantially high valued current is produced by circular short 16. The impedance of line 21 is a function of the spacing between plate 12 and face 17a and the impedance of transmission line 22 is of substantially low value.

Since line 22 is hollow, the length of this line becomes an active part of the total cavity. Resonator appears to the applied signal as presenting a true short comprising face 17 of plunger 14 together with the circular short at open end 19a with respect to wall 11. Thus, resonator 10 does not appear as having a true'cylindrical shape but is somewhat restricted in the area of plunger 14. This has the effect of compressing the total cavity for a given resonance. Accordingly, with wall 19 part of the length of the resonant cavity, there is achieved an advantage of substantially little unused room within resonator 10 needed to accomodate the re-entrant choke.

In summary, it will now be understood that radial plate 12 is required in order to provide a constant gap between plunger 14 and plate 12 forming line 21 with short 16.-Without plate 12 as plunger 14 were moved up and down, the impedance of line 21 would vary, thereby varying the position of the short. Therefore, the impedance of radial line 21 is a fucntion of the distance between plate 12 and plunger 14. It will be understood that the impedance of line 21 affects the efficiency of the choke.

Since resonator 10 may be used over a broad band range of frequencies, as for example 960-1,215 MI-Iz, the reflected short at edge 19a may vary in position above or below the edge to a tolerable limit. A tolerable limit may be, for example, one-eighth inch. How ever, if the short is reflected beyond that limit, as for example up into the plunger or beyond the end of the plunger, there is a degredation of the unloaded Q.

The choke assembly comprising plunger 14 and plate 12 may be raised or lowered by conventional screw mechanisms. However, conventional mechanisms have taken up much room above resonator top 30 which defines the approximate maximum height of the choke assembly. In order to reduce to a minimum this room taken above top 30, there is provided elevation mechanism 100 shown in FIGS. 2, 3, 5 and 6 for raising and lowering plunger 14 and plate 12 bidirectionally in substantially vertical displacement. In these figures, it will be seen that plate 12 and plunger 14 are secured each to the other through bolts 160 passing through plate openings 162 and passages 164 in boss as shown in FIG. 2. In this manner, the plate and plunger are slaved to each other when they are displaced by elevation mechanism 100.

Knurled knob 106, shown in FIG. 3 is manually rotatable in a plane substantially normal to the verticaldisplacement direction. In operation, knob 106 turns drive gear 108 through connecting drive shaft 110. Drive shaft 110 is rotatably moveable but constrained within through passages of upper and lower block 112, 113 which are secured to basic assembly outside cylindrical wall 101. Drive shaft 110 may be force fit through drive gear 108, mounted by bolts, or like manner, or be formed as a portion of gear 108 in one piece. Gear 108 includes longitudinally extended teeth members to interface with ring gear 118.

Pin members 114 mounted to shaft lock 116 are slideable insertable within upper block 112 in a vertical direction to provide a mechanism for locking drive gear 108 at a predetermined point .in its rotation responsive to the rotation of knob 106. In operation, knob 106 may be lifted in the vertical direction through release of pin members 114 from insertion contact with upper block 112. This releases knob 106 from constrainment with block 112 and permits free rotation thereof. Knob 106 is then rotated, which moves drive shaft 110 and elongated drive gear 108. Drive gear 108 is mated to ring gear 118 which is correspondingly rotated responsive to the movement of knob 106.

After ring gear 118 has been moved through a desired rotation, knob 106 is forced in a downward direction to engage pin members 114 within block 112 to fixedly restrain gear 118 in the predetermined orientation.

As shown in FIG. 6, ring gear 118 interfaces with spindle gear 120 having vertically directed tooth members. Additionally, ring gear 118 is mounted within spindle gear 120 and positionally retained between upper and lower spindle gear walls 121. Therefore, gear 120 takes the geometric contour of a spool member having vertically directed teeth on a peripheral surface between walls 121. Ring gear 118 includes shoulders 123 which provide for mating with walls 121, shown in FIG. 3. This mounting of gear 1 18 to 120 provides for vertical constrainment of ring gear 118 while permitting rotation in a horizontal plane.

As shown in FIG. 6, spindle gear 120 is rigidly mounted to an outer wall of sleeve or spindle tube 122. Gear retainer 124 is securely mounted to sleeve 122 and spindle gear 120 at a lower surface thereof. Retainer 124'maintains spindle gear 120 in a vertically fixed position. Sleeve 122 passes through a vertically directed opening of top bracket 126 which is rotatably moveable with respect to sleeve 122 on a lateral surface thereof and further moveable with respect to spindle gear 120 through a set of ball bearings 128.

It is therefore seen that bracket 126 may remain fixed as spindle gear 120 and sleeve 122 are rotated. Thrust ring 130 is fixedly secured to sleeve 122 and is moveably displaceable with respect to top bracket 126 through an upper set of ball bearings 128 as shown in FIG. 6. Additionally, top bracket 126 is securely mounted on opposing transverse ends to a pair of compensating rods 131 which extend in the vertical direction as shown. Bolts 132 secure bracket 126 to opposingly positioned compensating rods 131 which are fixedly positioned as spindle gear 120 is rotated. Upper sleeve nut threadedly engages sleeve 122 and provides a stop for the vertical displacement of sleeve 122.

Sleeve 122 threadedly engages fixed bolt 134 on an inner surface thereof. Bolt 134 includes a threaded portion as shown and is fixedly secured to the outer casing at bolt upper and lower sections 136, 138 respectively. Thus, bolt 134 remains positionally fixed as spindle. gear 120 is rotated responsive to the motion of ring gear 118. However, the rotation of spindle gear 120 and sleeve 122 causes a vertical displacement of sleeve 122 with respect to bolt 134 and all attached members.

Parallel displaced compensating rods 131 are mounted to bottom bracket 140 through lower bolts 142 as shown. Additionally, moveable rod 144 is secured to bracket 140 at one transverse end thereof. Since bottom bracket 140 is fixedly constrained to top bracket 126 through compensating rods 131, itis seen that movement or rotation of spindle gear 120 will cause a corresponding vertical displacement of bottom bracket 140 and rod 144.

Rod 144 passes vertically into chamber 146 as is shown in FIG. 5 and 6. Vacuum value 148 extends through a side wall of vacuum housing 154 to'provide a means for evacuating chamber 146 and cavity 100. Bellows 150 is attached to block 152 which in turn surrounds and is secured to rod 144. On an opposing end, bellows 150 is secured to a lower surface of housing 154 and permits displacement of rod 144 while maintaining an evacuated condition within chamber 146 and cavity a. In this manner, it is seen that rod 144 is moveably displaceable in a vertical direction responsive to the movement of gear 120 and corresponding rotation of ring gear 118 through manually turning of knob 106;

The material compositions of compensating rods 131 also provide for a thermal compensation mechanism within the assembly. As temperature increases, side wall 101-increases in height thereby increasing the cavity 10a height. In order to minimize this expansion, rods 131 are formed of a high thermal coefficient material such as aluminum, brass or some like composition. In contrast, fixed bolt 134 is formed of a material having a low coefficient of thermal expansion such as Invar. Thus, as temperature rises, wall 101 extends, however rods 131 move downwardly causing rods'144 to move in the same direction. This reduces the height of cavity 10a to compensate for the initial temperature increase.

Three rods are mounted to plate 12 through three Each bracket 156 extends through an opening 170, FIGS. 5-6, and is secured to corresponding rod 144 on an, end of each bracket. Each bracket extends in. a radial direction from a peripheral wall ofplate 12. Each of the three brackets 156 interface with and are secured to a corresponding bracket 158 as shown in FIG. 2. Each of the three brackets 158 are then mounted to an upper surface of plate 12. and a corresponding bracket 156. This mounting then produces a rigid connection between plate 12 and rods 144. It is therefore seen that as rod 144 is vertically displaced, plate 12 and attached plunger 14 are correspondingly displaced in a vertical direction.

It is to be understood that three elevating mecha-- having a side wall with an upper and a lower end comprising,

a plunger formed of an open hollow cylinder having an open end and a closed end, said open end facing in a direction into said cavity,

a radial plate secured to said closed end on the side thereof remote from said open end forming between said radial plate and said remote side, a radial transmission line terminated in a short which short is reflected through said radial transmission line and the outer periphery of said plunger as a short between said plunger open end and the wall,

means for displacing said radial plate and plunger comprising at least one bracket member secured to said radial plate and plunger and extending through an opening in said side wall of said cylindrical resonator, and

elevation means mounted to said bracket member external of said side wall between said side wall upper and lower ends for displacement of said radialplate and plunger in a substantially vertical direction.

2. The re-entrant radial choke of claim 1 in which said elevation means includes compensating rod means having a high "coefficient of thermal expansion for maintaining said cavity dimensions substantially constantas the temperature varies with respect to said radial choke.

3. The re-entrant radial choke of claim 2 in which said elevation means includes gearing means, movable member means secured to said bracket member, said compensating rod means being coupled between said gearing means and said movable member means.

4. The re-entrant radial choke of claim 3 in which said elevation means includes a vertically extending bolt member external of said side wall and said gearing means being threadedly mounted to said bolt member and rotatably movable with respect thereto.

5. The re-entrant radialchoke of claim 4 in which said movable member means includes a vertically extending rod having one end secured to said bracket, a

- bottom bracket secured to the other end of said vertitherein for allowing vertical movement of said bracket member, radial plate and plunger.

7. The re-entrant radial choke of claim 6 in .which there are provided three bracket members secured to said radial plate and plunger and in which there is provided elevation means for each of said bracket members.

8. The re-entrant radial choke oficlaim 2 in whichsaid open hollow cylinder forms a cylindrical wall with theopen bottom edge of said cylindrical wall facing into said cavity whereby said cylindricalwall is a part of the resonant cavity.

9. The re-entrant radial choke of claim 2 in which there is provided spacer means secured between said radial plate and said remote side of said closed end thereby forming said radial transmission line between an outer edge of said spacer means and said outer plunger periphery.

10. The re-entrant radial choke of claim 9 in which said outer edge is'circular in shape and defines a circular short and in which said radial transmission line and said outer plunger periphery form a one-half wavelength line.

11. The re-entrant radial choke of claim 10 in which said radial transmission line and the transmission line between said outer plunger periphery and said cavity wall, each form a one-quarter wavelength line.

12. The re-entrant radial choke of claim in which said spacer means comprises a boss formed on said remote side.

13. A re-entrant radial choke forming a variable non- 10 contacting reflecting short for terminating a cylindrically walled microwave cavity of a cylindrical resonator comprising,

a plunger formed of an open hollow cylinder having an open end and a closed end, said open end facing in a direction into said cavity,

a radial plate secured to said closed end onthe side thereof remote from said open end forming between said radial plate and said remote side, a radial transmission line terminated in a short which short is reflected through said radial transmission line and the peripheyy of said plunger as a short between said plunger open end and the cavity wall,

means for displacing said radial plate and said plunger in a substantially vertical direction for ad justing the vertical dimension of said cavity, said displacement means including:

a. a vertically extending bolt member passing external said cylindrical resonator;

b. gearing means threadedly mounted to said bolt member, said gearing means being rotatably movable with respect to said bolt member; and

c. a bracket mount member secured to said radial plate and said gearing means for displacement of said radial plate responsive to said rotatable movement of said gearing means.

14. The re-entrant radial choke of claim 13 where said gearing means includes:

a. a ring gear extending around the periphery of and external to said cylindrical resonator; and b. a spindle gear mated to said ring gear for rotational movement with respect to said bolt member responsive to rotational actuation of said ring gear, said spindle gear being secured to said bracket member for displacing said radial plate in said vertical direction.

15. The re-entrant radial choke of claim 13 wherein said bracket mount member includes at least one tem-.

perature compensation rod formed of a material having a high coefficient of thermal expansion for maintaining said cavity dimensions substantially constant when said cavity wall is subjected to temperature excursions.

PC1-1050 UNITED STATES PATENT OFFICE CERTIFICATE GE CQRRECTIGN Patent No. 3 a 806 s 8H2 Dated April 23 197 Inventor(s) R. F. Sleizin et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 13, lirie 13, change "peripheyy" to --outer periphery- Signed and sealed this 10th day of September 197A.

(SEAL) Attest:

MCCOY M. GIBSON, JR. 7 v I c. MARSHALL DANN v Attesting Officer Commissioner of Patents 

1. A re-entrant radial choke forming a variable noncontacting reflecting short for terminating a cylindrically walled microwave cavity of a cylindrical resonator having a side wall with an upper and a lower end comprising, a plunger formed of an open hollow cylinder having an open end and a closed end, said open end facing in a direction into said cavity, a radial plate secured to said closed end on the side thereof remote from said open end forming between said radial plate and said remote side, a radial transmission line terminated in a short which short is reflected through said radial transmission line and the outer periphery of said plunger as a short between said plunger open end and the wall, means for displacing said radial plate and plunger comprising at least one bracket member secured to said radial plate and plunger and extending through an opening in said side wall of said cylindrical resonator, and elevation means mounted to said bracket member external of said side wall between said side wall upper and lower ends for displacement of said radial plate and plunger in a substantially vertical direction.
 2. The re-entrant radial choke of claim 1 in which said elevation means includes compensating rod means having a high coefficient of thermal expansion for maintaining said cavity dimensions substantially constant as the temperature varies with respect to said radial choke.
 3. The re-entrant radial choke of claim 2 in which said elevation means includes gearing means, movable member means secured to said bracket member, said compensating rod means being coupled between said gearing means and said movable member means.
 4. The re-entrant radial choke of claim 3 in which said elevation means includes a vertically extending bolt member external of said side wall and said gearing means being threadedly mounted to said bolt member and rotatably movable with respect thereto.
 5. The re-entrant radial choke of claim 4 in which said movable member means includes a vertically extending rod haVing one end secured to said bracket, a bottom bracket secured to the other end of said vertically extending rod and compensating rod means being secured to said bottom bracket.
 6. The re-entrant radial choke of claim 5 in which said opening in said side wall defines a vertical opening therein for allowing vertical movement of said bracket member, radial plate and plunger.
 7. The re-entrant radial choke of claim 6 in which there are provided three bracket members secured to said radial plate and plunger and in which there is provided elevation means for each of said bracket members.
 8. The re-entrant radial choke of claim 2 in which said open hollow cylinder forms a cylindrical wall with the open bottom edge of said cylindrical wall facing into said cavity whereby said cylindrical wall is a part of the resonant cavity.
 9. The re-entrant radial choke of claim 2 in which there is provided spacer means secured between said radial plate and said remote side of said closed end thereby forming said radial transmission line between an outer edge of said spacer means and said outer plunger periphery.
 10. The re-entrant radial choke of claim 9 in which said outer edge is circular in shape and defines a circular short and in which said radial transmission line and said outer plunger periphery form a one-half wavelength line.
 11. The re-entrant radial choke of claim 10 in which said radial transmission line and the transmission line between said outer plunger periphery and said cavity wall, each form a one-quarter wavelength line.
 12. The re-entrant radial choke of claim 10 in which said spacer means comprises a boss formed on said remote side.
 13. A re-entrant radial choke forming a variable noncontacting reflecting short for terminating a cylindrically walled microwave cavity of a cylindrical resonator comprising, a plunger formed of an open hollow cylinder having an open end and a closed end, said open end facing in a direction into said cavity, a radial plate secured to said closed end on the side thereof remote from said open end forming between said radial plate and said remote side, a radial transmission line terminated in a short which short is reflected through said radial transmission line and the peripheyy of said plunger as a short between said plunger open end and the cavity wall, means for displacing said radial plate and said plunger in a substantially vertical direction for adjusting the vertical dimension of said cavity, said displacement means including: a. a vertically extending bolt member passing external said cylindrical resonator; b. gearing means threadedly mounted to said bolt member, said gearing means being rotatably movable with respect to said bolt member; and c. a bracket mount member secured to said radial plate and said gearing means for displacement of said radial plate responsive to said rotatable movement of said gearing means.
 14. The re-entrant radial choke of claim 13 where said gearing means includes: a. a ring gear extending around the periphery of and external to said cylindrical resonator; and b. a spindle gear mated to said ring gear for rotational movement with respect to said bolt member responsive to rotational actuation of said ring gear, said spindle gear being secured to said bracket member for displacing said radial plate in said vertical direction.
 15. The re-entrant radial choke of claim 13 wherein said bracket mount member includes at least one temperature compensation rod formed of a material having a high coefficient of thermal expansion for maintaining said cavity dimensions substantially constant when said cavity wall is subjected to temperature excursions. 